Variable resistor means

ABSTRACT

A variable resistor unit particularly useful in selectively controlling current in a circuit of low or medium voltage, a preferred form of the invention includes a smooth bore resistance coil having a helical wire contact element convolutely arranged in the bore of the resistance coil structure of the device. A ring of metallic mercury fluid is concentrically arranged in the bore of the resistance coil and defines adjustable contact means engaging the contact areas of the helical coil element. Selective axial manipulation of the mercury ring in the bore of the resistance coil operatively increases or decreases the resistance in the circuit of the resistor device.

United States Patent Inventors James W. Gibbs 8027 W. 14th Avenue; John L. Gibbs, 14820 Miami Lakeway East, both of Hialeah, Fla. 33014 [2| I Appl. No. 21,794 [22] Filed Mar. 23, X970 [45] Patented Aug. 3, I971 [54 1 VARIABLE RESISTOR MEANS 10 Claims, 3 Drawing Figs.

[52] US. Cl 338/156,

338/ M3 [5|] Int. Cl Hole 9/00 [50] Field of Search 338/156, 143, I49, 177,27, 38,94,151

[56] References Cited UNITED STATES PATENTS 2,086,455 7/l937 Wilson 338/l 77 X Primary Examiner-Lewis H. Myers Assistant Examiner-D. A. Tone Att0rneyJohn Cyril Malloy ABSTRACT: A variable resistor unit particularly useful in selectively controlling current in a circuit of low or medium voltage, a preferred form of the invention includes a smooth bore resistance coil having a helical wire contact element convolutely arranged in the bore of the resistance coil structure of the device. A ring of metallic mercury fluid is concentrically arranged in the bore of the resistance coil and defines adjustable contact means engaging the contact areas of the helical coil element. Selective axial manipulation of the mercury ring in the bore of the resistance coil operatively increases or decreases the resistance in the circuit of the resistor device.

cavity, the likelihood of the i The contact surfaces of the VARIABLE RESISTOR MEANS BACKGROUND OF THE INVENTION The broad concept of utilizing metallic mercury fluid as the movable electric contact component in electrical devices is not new. The US. Pat. Nos. 1,908,908 2,647,975 illustrate the use of metallic mercury contact means as the movable contact component of electric switch and rheostat devices. The several advantages of utilizing captivated metallic mercury as an electrical contact is well known to those working in the art. A fluid mercury contact element permits a positive electrical connection between the contact points of the switch or rheostat element and with a minimum of contact pressure between the elements. Mercury fluid contactsare substantially friction free; wear and attrition at the contact engagement is substantially obviated. A principal disadvantage ofthe fluid mercury contact means is that of maintaining the fluid mecury mass in captivated form during operation or selective adjustment of an,electrical device. As is illustrated in US. Pat. Nos. 1,908,908 and 2,647,975, a mercury contact in small gobule form is contained in a socket disposed in the distal end of a movable contact arm. In such prior art, the mercury fluid principallyis maintained in operative form by virtue of the characteristics of the fluid. The molecular structure and surface tension of the mercury fluid defines the principal means for maintaining the mercury in operative configuration. In a prior art switch or rheostat device subjected to rough service,

a fluid mercury contact may be shattered and the electrical device rendered inoperative. Also, the prior art mercury contact devices tended to discolor function ofthe resistor'or rheostat device.

SUMMARY OF INVENTION and oxidize, thus impairing the fluid mercury contact means and substantially obviates many of the above-mentioned disadvantages. In the instant invention, the mercury fluid is maintained in annular configuration by form means completely enclosing and fully captivating the mercury fluid contact means; the fluid mercury is maintained in operative form without regard to the molecular structure or surface tension characteristics of the mercury fluid. By operatively maintaining the mercury fluid in substantially a sealed mercury shattering'and the electrical device becoming inoperative, is substantially obviated. instant invention preferably are hemispherically enclosed in an inert gas thereby obviating oxidation of the contact surfaces andincreasing thedurability and efficiency ofthe device.

BRIEF DESCRIPTIONOF THE DRAWINGS FIG. 1 is a longitudinal sectional view of the variable resistor device of the instant invention;

FIG. 2 is a transverse sectional view taken as on the line 2-2 ofFlG.ll;and

FIG. 3 is an enlarged sectional view taken as on the line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT body 22 and the cylindrical The frame structure 16 of the resistance coil assembly 14 is generally sleevelike and formed of material nonconductive of electricity. The helical wire resistance element 18 preferably is embeddedly formed concentrically in the tubular frame structure 16 and with the helical interior surfaces 43 of the helical wire element 18 being in axial alignment with the cylindrical bore surface 44 of the resistance coil frame 16. In the preferred form of the invention, the helical wire element 18 in addition to defining the resistance means ofthe device 12, also defines primary contact means for directly engaging the,

secondary contact mercury ring 30. The interior helical contact surfaceareas 43 of the helical resistance element 18 is operatively engageable with the mercury ring 30 and defines infinitely variable resistance means effective substantially throughout the helical length of the wire resistance element.

In certain embodiments of the invention (not shown) the coil means 18 may be fully embedded in the tubular frame structure 16, and the contact surface areas 43 may be intermittently radially and axially disposed in the bore 20; however in the preferred form of the invention (as shown) the helical wire resistance element 18 defines also the contact surface areas 43 operative in direct engagementwith the mercury ring structure 30. In the alternate embodiment (not shown) an intermittent arrangement of the contact surfaces 43 in the bore 20 will provide a stepped or incremental adjustment of the resistance in a circuit. The cylindrical interior surface 44 of the tubular frame 16 defines an annular surface area 46 displaced axially relative to the resistance coil element 18 and defines an off position for the secondary contact mercury ring 30, and a disposition deenergizing the circuit ofelectric leads 34, 38.

The disclike body-22 of the mercury form means fitted in the bore 20 of the resistance coil construction 14 preferably is formed of material nonconductive of electricity and is threadedly fitted on the forward distalend of the control rod 40 along internal external mating threads 48. A circular pair of grooves 50, 50 are formed in the circular periphery of the body 22 and defines retainer groove means for retaining the resilient O-rings 24, 24 (see ,FIG. 3). The O'ring pair 24,24 are sealingly arranged interposedly between the mercury form surface of the resistance coil bore 20 and defines annular chamber means sealingly containing the annular mass of mercury fluid of the mercury ring 30.

I The primary conductor means 32 preferably is in the form of a terminal stud 52 having one end area fused at 54 to the proximal end portion 56 of the helical resistance element 18. The opposite end portion of the terminal stud 52 is adapted to be connected with a positive potential in a circuit, as for example the potential ofelectric lead 34.

The secondary conductor means 36 is adapted for connecting the mercury ring 30 with a negative potential of an electric circuit, as represented by the electric lead 38 in FIG. I. The secondary conductor means preferably includes a wire loop 60 fitted in the mercury form body 22; a terminal stud 62 fixedly secured in the tubular frame 16; and a flexible connector wire 64 convolutely loosely arranged about the control rod 40 and attached at attachment points 66, 68 respectively to the mercury body 22 and terminal stud 62. The small gauge wire loop 60 is fitted in the bottom of the central groove 70 of the disc body 22 and substantially continuously electrically engages the circular extension ofthe mercury ring. Push and pull manipulation of the control rod 40 and thus the mercury contact 30, is permitted respectively by helical expansion and contraction of the flexible connector wire 64.

A bearing cup 72 preferably is coaxially attached to the rearward portion of the tubular frame 16 by screw means 74 I and provides bearing structure 76 for supporting the rearward the mercury ring 30 with an electric lead 38; and, control rod and handgrip means 40, 42 connected with the disclike body 22 and providing means for adjustably positioning the mercury ring within the bore 20 ofthe resistance coil assembly.

p'or'tiori'ofthe control rod '40 during the push and pull manipulation thereof. The variable resistor device 12 preferably includes means hermetically containing a quantity ofelectrically inert gas in the bore 20 of the'resistance coil assembly 14 for retarding" or obviating the oxidation of the primary contact surfaces 43 of the helical wire element 18 during operation of the device. The terminal studs 52, 62 are preferablv sealinolv fitted in the tubular frame 16. A cover plate 78 is fixedly sealingly secured to the forward face of the tubular frame 16 by screw means 80. A cuplike bellows member 82 is concentrically fitted in the bearing cup 72; the rearward end 84 of the bellows 72 is sealingly fitted concentrically on the control rod 40; the annular forward rim portion 86 of the bellows 72 is in terposedly clampingly secured between the bearing cup 72 and tubular frame 16 by the screws 74. Electrically inert gas is introduced into the interior of the resistance coil assembly 14 and hermetically sealed by suitable means. A passageway 88 extends through the disc body 22 and provides means for equalizing pressure of the inert gas on opposite sides of the pair of O-rings 24, 24 during the push pull manipulation of the control rod.

In using the variable resistor device, the current of electric leads 34, 38 is energized by pushing the control rod inwardly and electrically engaging the mercury ring 30 with the distal portion 90 of the helical wire element 18. The resistance in the circuit of electric leads 34, 38 may be varied by selective movement of the control rod and thus selective positioning of the mercury ring 30 along the helical extension of the wire resistance element 18. Progressive inward movement of the control rod decreases the resistance in the circuit. Conversely, progressively pulling outwardly on the control rod increases the resistance in the circuit. Moving the control rod fully inwardly arranges the mercury ring 30 in direct contact with the terminal stud 52 thereby negating the function of the helical resistance element 18 and disposing the circuit of electric leads 34, 38 in a low resistance condition. Moving the control rod outwardly axially displaces the mercury ring 30 from the helical wire element 18 and arranges the circuit in an open cir' cuit condition.

While the instant invention is shown and described in what is presently conceived as being the most preferred andpractical embodiment, it will be understood that various changes and modifications may be made of the disclosed embodiment without departing from the spirit and scope of the invention.

What we claim is:

1. Variable resistor means comprising smooth borere sistance coil means including a helical wire resistance element of material conductive of electricity, and tubular frame means adapted for connection with a negative potential of a circuit;

and, means operative in causing selective axial movement of said secondary contact means in said resistance coil means and selective positioning of said secondary contact means relative to said primary contact means.

2. Variable resistor coil means as set forth in claim 1 wherein said means for causing selective axial movement of said secondary contact means relative to said primary contact means includes contact rod means connected with said mercury form means and handgrip means fixed on the distal end of said control rod means for selective relative positioning of the primary and secondary contact means.

3. Variable resistor means as set forth in claim ll wherein the internal surface structure defining the smooth bore of said resistance coil means is defined in part by an annular surface area of electrically nonconductlve material disposed transversely of the coil means and at a disposition displaced axially relative to said resistance coil element.

4. Variable resistor means as set forth in claim 1 wherein said plurality of contact surface areas of said primary contact means are-defined substantially by radially inwardly oriented surface areas of the helical resistance coil element and wherein the mercury fluid of said secondary contact means directly engages certain contact surface areas of the wire coil element as the secondary contact means is selectively manipulated.

5. Variable resistor means as set forth in claim 4 wherein the plurality of contact surface areas of said primary contact means are substantially merged together successively along the helical extension of said resistance coil element substantially along its full extension, the arrangement defining infinitely variable resistance means extending substantially along the full helical length of the resistance coil element.

6. Variable resistor means as set forth in claim 1 wherein the bore of said resistance coil means is cylindrical 7. Variable resistor means as set forth in claim 6 wherein said form means includes a disclike body and a pair of O-rings .of re'silient materials snugly fitted concentrically on said disc body and defining substantially the external groove means of the form means, the ()-ring pair being sealingly arranged interposedly between the disc body and cylinder bore of said rehaving internal surface structure formed of material nonconmercury fluid and maintaining the fluid in constant contact with the bore of said resistance coil means; first conductor means having one end portion connected to mercury fluid and having the other end portion adapted for connection with a positive potential in a circuit; second conductor means having one end portion connected to one end portion of said resistance coil element and having the other end portion sistance coil means and defining substantially annular closed chamber means sealingly containing the mercury fluid.

8; Variable resistor means as set forth in claim 7 wherein said control rod means is of substantially small diameter and is coaxially fitted to the disc body of said mercury form means, and wherein said first conductor means includes a small flexible connector wire element convolutely loosely arranged about the control rod means.

9. Variable resistor means as set forth in claim 1 additionally including means hermetically containing a quantity of electrically inert gas in the bore of the resistance coil means.

10. Variable resistor means as set forth in claim 9 which includes a bellows member sealingly coaxially operatively interposed between said control rod means and said smooth bore resistance coil means and defining in part the means hermetically containing the inert gas in the bore of said resistance coil meansl 

1. Variable resistor means comprising smooth bore resistance coil means including a helical wire resistance element of material conductive of electricity, and tubular frame means having internal surface structure formed of material nonconductive of electricity; primary contact means including a plurality of contact surface areas arranged at least along the axial extension of said smooth bore coil means and electrically connected at least at intermittent intervals along he helical extension of said wire coil element; secondary contact means including a quantity of metallic mercury fluid, generally circular mercury form means snugly but freely fitted in the bore interior of said resistance coil means and having external groove means of the outer periphery of said form means receiving the mercury fluid and maintaining the fluid in constant contact with the bore of said resistance coil means; first conductor means having one end portion connected to mercury fluid and having the other end portion adapted for connection with a positive potential in a circuit; second conductor means having one end portion connected to one end portion of said resistance coil element and having the other end portion adapted for connection with a negative potential of a circuit; and, means operative in causing selective axial movement of said secondary contact means in said resistance coil means and selective positioning of said secondary contact means relative to said primary contact means.
 2. Variable resistor coil means as set forth in claim 1 wherein said means for causing selective axial movement of said secondary contact means relative to said primary contact means includes contact rod means connected with said mercury form means and handgrip means fixed on the distal end of said control rod means for selective relative positioning of the primary and secondary contact means.
 3. Variable resistor means as set forth in claim 1 wherein the internal surface structure defining the smooth bore of said resistance coil means is defined in part by an annular surface area of electrically nonconductive material disposed transversely of the coil means and at a disposition displaced axially relative to said resistance coil element.
 4. Variable resistor means as set forth in claim 1 wherein said plurality of contact surface areas of said primary contact means are defined substantially by radially inwardly oriented surface areas of the helical resistance coil element and wherein the mercury fluid of said secondary contact means directly engages certain contact surface areas of the wire coil element as the secondary contact means is selectively manipulated.
 5. Variable resistor means as set forth in claim 4 wherein the plurality of contact surface areas of said primary contact means are substantially merged together successively along the helical extension of said resistance coil element substantially along its full extension, the arrangement defining infinitely variable resistance means extending substantially along the full helical length of the resistance coil element.
 6. Variable resistor means as set forth in claim 1 wherein the bore of said resistance coil means is cylindrical
 7. Variable resistor means as set forth in claim 6 wherein said form means includes a disclike body and a pair of O-rings of resilient materials snugly fitted concentrically on said disc body and defining substantially the external groove means of the form means, the O-ring pair being sealingly arranged interposedly between the disc body and cylinder bore of said resistance coil means and defining substantially annular closed chamber means sealingly containing the mercury fluid.
 8. Variable resistor means as set forth in claim 7 wherein said control rod means is of substantially small diameter and is coaxially fitted to the disc body of said mercury form means, and wherein said first conductor means includes a small flexible connector wire element convolutely loosely arranged about the control rod means.
 9. Variable resistor means as set forth in claim 1 additionally including means hermetically containing a quantity of electrically inert gas in the bore of the resistance coil means.
 10. Variable resistor means as set forth in claim 9 which includes a bellows member sealingly coaxially operatively interposed between said contRol rod means and said smooth bore resistance coil means and defining in part the means hermetically containing the inert gas in the bore of said resistance coil means. 